Sensitivity of the Dynamic Response of Monopile-Supported Offshore Wind Turbines to Structural and Foundation Damping

Abstract

The prediction of ultimate and fatigue demands for the design of offshore wind turbines (OWTs) requires accurate simulation of the dynamic response of OWTs subject to time-varying wind and wave loads. The magnitude of damping in an OWT system significantly influences the dynamic response, however, some sources of damping, such as foundation damping, are not explicitly considered in design guidelines and may increase damping significantly compared to commonly assumed values in design. Experimental and analytical studies have estimated the magnitude of foundation damping to be between 0.17% and 1.5% of critical, and this paper investigates how increased damping within this range affects load maxima and fatigue damage for a hypothetical 5MW OWT subjected to a variety of wind, wave, and operational conditions. The paper shows that increased damping effects the greatest percentage reduction of ultimate moment demands and fatigue damage when the OWT rotor is parked and feathered. In such cases, the aerodynamic damping is relatively low, allowing for additional damping from the foundation to account for a relatively larger proportion of the total system damping. Incorporating foundation damping in design guidelines may lead to more efficient structures, which is a crucial factor in overcoming the high cost barrier associated with offshore wind development.

Scour influence on the fatigue life of operational monopile‐supported offshore wind turbines

“…This paper investigates the FL of a 5‐MW wind turbine model with properties provided by the US National Renewable Energy Laboratory (NREL) . Various studies have been based on this wind turbine as a significant amount of data is available for it . In this study, different software packages were used for the fatigue analysis, as shown in Figure .…”

“…30 Various studies have been based on this wind turbine as a significant amount of data is available for it. [31][32][33][34][35][36][37] In this study, different software packages were used for the fatigue analysis, as shown in Figure 1. The preprocessing module TurbSim was used to model the turbulent incoming wind field as an input to FAST.…”

Fatigue life sensitivity of monopile-supported offshore wind turbines to damping

“…The influence of damping on the fatigue damage of offshore wind turbines has been mostly considered in parked/non-operational conditions in the literature. The fatigue assessment of OWT is usually carried out by simulating and analysing the stress at critical locations such as the tower base [25,26] or the mudline [27]. The effect of damping in a parked condition was studied and it was demonstrated that the maximum bending moment could increase by 20% as a result of a 50% change in damping [6].…”

“…The effect of soil damping has been studied and up to 47% reduction in fatigue damage due to a 4% increase in soil damping has been reported [26]. It was also suggested that a complete lifetime simulation including damping effects could clarify the influence on the fatigue life of OWTs, which has not been reported in literature.…”

Modelling damping sources in monopile‐supported offshore wind turbines

“…Therefore, it is essential to quantify properly the damping from different sources to assess the fatigue damage of an OWT. There are 5 main sources of damping in OWTs: aerodynamic, hydrodynamic, structural, soil, and supplemental damping provided by mechanical dissipating devices . As OWTs are lightly damped structures, it is usual to assume that the total damping factor in the system is simply the sum of the damping factors from different sources as expressed by Equation : where ζ Total , ζ Aero , ζ Struc , ζ Hydro , ζ Soil , and ζ Damper are respectively the total, aerodynamic, structural, hydrodynamic, soil, and supplemental damping factors as a percentage of critical damping.…”